[Effect of metoprolol on the circulation after head trauma. Studies during continuous intravenous administration...

The influence of continuous intravenous administration of metoprolol on heart rate and haemodynamics was tested in ten unconscious patients who, after sustaining a head injury, developed sinus tachycardia due to increased sympathicotonia. In preliminary studies on three patients the effective dosage for heart rate reduction was determined. Following this, seven patients received 0.15 mg/kg . h of metoprolol over 36 hours. Heart rate decreased from an average of 127.5 to 78.8/min, a statistically significant reduction. Stroke volume index significantly rose from an average of 35.5 to 52.3 ml/m2, while other haemodynamic variables were not or only slightly changed. Cardiac index fell (not significantly) from 4.51 to 3.81/min . m2, peripheral vascular resistance rose (not significantly) form 942.4 to 1061.7 dyn . s . cm-5. Arterial and pulmonary artery pressures as well as filling pressures of right and left ventricle and left ventricular work index were not altered. Total oxygen consumption and oxygen extraction rate also remained unchanged. Measurement of metoprolol plasma levels in four patients excluded the possibility of a cumulative effect.